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<div class="titlepage"><div><div><h5 class="title">
<a name="beast.ref.boost__beast__basic_stream.async_read_some"></a><a class="link" href="async_read_some.html" title="basic_stream::async_read_some">basic_stream::async_read_some</a>
</h5></div></div></div>
<p>
          <a class="indexterm" name="idm14672"></a>
        </p>
<p>
          Read some data asynchronously.
        </p>
<h6>
<a name="beast.ref.boost__beast__basic_stream.async_read_some.h0"></a>
          <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_read_some.synopsis"></a></span><a class="link" href="async_read_some.html#beast.ref.boost__beast__basic_stream.async_read_some.synopsis">Synopsis</a>
        </h6>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
    <span class="keyword">class</span> <a href="../../../../../../../doc/html/boost_asio/reference/MutableBufferSequence.html" target="_top"><span class="emphasis"><em>MutableBufferSequence</em></span></a><span class="special">,</span>
    <span class="keyword">class</span> <a href="../../../../../../../doc/html/boost_asio/reference/ReadHandler.html" target="_top"><span class="emphasis"><em>ReadHandler</em></span></a> <span class="special">=</span> <span class="identifier">net</span><span class="special">::</span><span class="identifier">default_completion_token_t</span><span class="special">&lt;</span><a class="link" href="executor_type.html" title="basic_stream::executor_type">executor_type</a><span class="special">&gt;&gt;</span>
<a href="../../../../../../../doc/html/boost_asio/reference/asynchronous_operations.html#boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type" target="_top"><span class="emphasis"><em>DEDUCED</em></span></a>
<span class="identifier">async_read_some</span><span class="special">(</span>
    <span class="identifier">MutableBufferSequence</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">buffers</span><span class="special">,</span>
    <span class="identifier">ReadHandler</span><span class="special">&amp;&amp;</span> <span class="identifier">handler</span> <span class="special">=</span> <span class="identifier">net</span><span class="special">::</span><span class="identifier">default_completion_token_t</span><span class="special">&lt;</span> <a class="link" href="executor_type.html" title="basic_stream::executor_type">executor_type</a> <span class="special">&gt;{});</span>
</pre>
<h6>
<a name="beast.ref.boost__beast__basic_stream.async_read_some.h1"></a>
          <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_read_some.description"></a></span><a class="link" href="async_read_some.html#beast.ref.boost__beast__basic_stream.async_read_some.description">Description</a>
        </h6>
<p>
          This function is used to asynchronously read data from the stream. This
          call always returns immediately. The asynchronous operation will continue
          until one of the following conditions is true:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              One or more bytes are read from the stream.
            </li>
<li class="listitem">
              An error occurs.
            </li>
</ul></div>
<p>
          The algorithm, known as a <span class="emphasis"><em>composed asynchronous operation</em></span>,
          is implemented in terms of calls to the next layer's <code class="computeroutput"><span class="identifier">async_read_some</span></code>
          function. The program must ensure that no other calls to <a class="link" href="read_some.html" title="basic_stream::read_some"><code class="computeroutput"><span class="identifier">read_some</span></code></a> or <a class="link" href="async_read_some.html" title="basic_stream::async_read_some"><code class="computeroutput"><span class="identifier">async_read_some</span></code></a> are performed
          until this operation completes. If the timeout timer expires while the
          operation is outstanding, the operation will be canceled and the completion
          handler will be invoked with the error <a class="link" href="../boost__beast__error.html" title="error"><code class="computeroutput"><span class="identifier">error</span><span class="special">::</span><span class="identifier">timeout</span></code></a>.
        </p>
<h6>
<a name="beast.ref.boost__beast__basic_stream.async_read_some.h2"></a>
          <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_read_some.parameters"></a></span><a class="link" href="async_read_some.html#beast.ref.boost__beast__basic_stream.async_read_some.parameters">Parameters</a>
        </h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                  <p>
                    Name
                  </p>
                </th>
<th>
                  <p>
                    Description
                  </p>
                </th>
</tr></thead>
<tbody>
<tr>
<td>
                  <p>
                    <code class="computeroutput"><span class="identifier">buffers</span></code>
                  </p>
                </td>
<td>
                  <p>
                    The buffers into which the data will be read. If the size of
                    the buffers is zero bytes, the operation always completes immediately
                    with no error. Although the buffers object may be copied as necessary,
                    ownership of the underlying memory blocks is retained by the
                    caller, which must guarantee that they remain valid until the
                    handler is called.
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    <code class="computeroutput"><span class="identifier">handler</span></code>
                  </p>
                </td>
<td>
                  <p>
                    The completion handler to invoke when the operation completes.
                    The implementation takes ownership of the handler by performing
                    a decay-copy. The equivalent function signature of the handler
                    must be:
                  </p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span>
    <span class="identifier">error_code</span> <span class="identifier">error</span><span class="special">,</span>               <span class="comment">// Result of operation.</span>
    <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span>   <span class="comment">// Number of bytes read.</span>
<span class="special">);</span>
</pre>
                  <p>
                    Regardless of whether the asynchronous operation completes immediately
                    or not, the handler will not be invoked from within this function.
                    Invocation of the handler will be performed in a manner equivalent
                    to using <code class="computeroutput"><span class="identifier">net</span><span class="special">::</span><span class="identifier">post</span></code>.
                  </p>
                </td>
</tr>
</tbody>
</table></div>
<h6>
<a name="beast.ref.boost__beast__basic_stream.async_read_some.h3"></a>
          <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_read_some.remarks"></a></span><a class="link" href="async_read_some.html#beast.ref.boost__beast__basic_stream.async_read_some.remarks">Remarks</a>
        </h6>
<p>
          The <code class="computeroutput"><span class="identifier">async_read_some</span></code> operation
          may not receive all of the requested number of bytes. Consider using the
          function <code class="computeroutput"><span class="identifier">net</span><span class="special">::</span><span class="identifier">async_read</span></code> if you need to ensure that
          the requested amount of data is read before the asynchronous operation
          completes.
        </p>
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        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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